Device for tesiprinting



Feb. 15, 1966 E. M. VAN WAGNER 3,234,904

DEVICE FOR TESIPRINTING Filed June 15, 1962 2 Sheets-Sheet 1 IIIII'IIIIIIIIII'IIIIII,

. INVENTOR. EDWARD M. VAN WAGNER A 77'ORNEV Feb. 15, 1966 VAN WAGNER 3,234,904

DEVICE FOR TESIPRIN'IING 2 sheets 2 Filed June 5 R m m c T A N W E V W N m M D m W D E 3 6 5 N 0000000 EQQQ ATT NEV United States Patent Xerox Corporation, Rochester, N.Y., a corporation of New York Filed June 15, 1962, Ser. No. 202,900 2 Claims. (Cl. 118638) This invention relates in general to electrostatic recording and, in panticular, to an improved device for TESI- printing.

As originally conceived and disclosed in US. Patent 2,297,691 to Carlson and later related patents, latent electrostatic image are generally formed for use in the graphic arts by charging a photoconductive insulating member to sensitize it and then subjecting it to a light image or other pattern of activating electromagnetic radiation which serves to render it relatively conductive in radiation struck areas, thereby dissipating charge in those areas and leaving a charge pattern conforming .to the electromagnetic radiation pattern. Thus, a uniform change pattern is placed over the whole surface of the photoconductor and selectively dissipated in accordance with the image to 'be reproduced. The image is then developed or made visible by the deposition thereon of electros-tatically attracta ble finely divided colored material referred to in the art as toner.

More recently, it has been found that electrostatic latent images may advantageously be formed upon insulating mediums by controlled or selective charging from a shaped electrode thereby eliminating the need for a photoconductor and an exposure step. Since the low photographic speed of the photoconductors had been the main speed limiting factor in the formation of electrostatic images, it has been found that this new method of image formation known as TESI-printing is virtually instantaneous in its response and is well adapted for the recording of conventional coded electric signals including high speed alphanumeric computer output printing, high speed facsimile output printing, or the like. Typical applications of TESI-printing are disclosed in US. Patents 2,919,967 and 2,978,968 to Schwertz, and in copendapplication S.N. 683,647 filed September 12, 1957, by F. A. Sch-wertz, now US. Patent 3,076,968. Since TESI- printing produces a latent electrostatic image in the shape of the electrode used, image shape is limited only by the shape of the electrode or electrode combinations which may be produced.

These TESI-printing devices form latent electrostatic charge patterns in the desired configuration. In order to see these charge patterns on the insulating medium, they must be developed or made visible by allowing them to collect colored finely divided electroscopic material, known in .the art as toner, at a developing station, generally requiring both temporal and spatial separation between change printing and image visibility.

It is an object of this invention to define a novel TESI- printing system which produces an immediately visible image.

It is a further object of this invention to define a novel TESI-printing method.

It is another object of this invention to define a novel TESI-printing system embodying simultaneous printing and development which may be operated at high speeds.

It is also an object of this invention to define a novel T-ESI-printing system which may use a wide variety of developing materials.

The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of specific embodiments of the invention, especially when 3,234,904 Patented Feb. 15, 1966 taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a sectional view through a stationary apparatus embodying the novel printing technique of this invention.

FIGURE 2 is a section view taken along lines 2-2 of FIGURE 1.

FIGURES 3 and 4 are side and perspective views respectively illustrating the application of the printing technique of this invention to a high speed alphanumeric TESI-printing cylinder for line-at-a-time printing.

FIGURE 5 illustrates an embodiment of this invention utilizing a pin matrix TESI-printer.

FIGURE 6 is a plan view of the pin matrix of FIG- URE 5.

In FIGURE 1, which illustrates a relatively simple apparatus to facilitate describing the concept of this invention, there is shown a metallic backing electrode 11. Opposite and spaced from backing electrode 1 1 is an electrode 12 having raised portions 13 in the form of the character to be printed. This is shown more clearly in FIGURE 2 which is a view of the face of the electrode taken along section lines 2-2 of FIGURE 1. Alternatively, the whole electrode may be in the form of the character to be printed and may optionally be surrounded with insulating material on its sides, so that the electrode and insulating material have a flush face. Although backing electrode 11 may have a roughened or grained surface and may even be in the form of a screen, it has a relatively smooth surface ascompared with the hills and Valleys formed by the raised portions 13 on the character electrode 12. A portion of the printing member 15 is shown in the gap formed by the two opposed electrodes 11 and 12. As shown in this view the printing member 15 is made up of a layer of paper 16 overcoated with a thin layer of insulating material 17 such as CYMAC, an alkyd resin available from American Cyanamid Corporation. Instead of CYMAC, any good dielectric material may be used including cellulose triacetate, polyethylene terephthalate (Mylar) or the like. A uniform layer of developing material 18 made up of finely divided particles is coated on the upper surface of backing electrode 11. It should be appreciated that considerably more material would be present than is shown in this illustration. This developing material shown in this view is made up of negatively charged insulating par-ticles. However, the polarity of charge selected for the developing particles is dependent on the polarity of the pulse applied to transfer these particles and the electrode to which it is applied. Insulating particles of the type generally used in Xerographic development are suitable for use with this invention. Such particles, known in the art as toners, generally have average particle size of about 4 to 10 microns. Particles of this type are more fully described in US. Patent 2,891,011 to Insalaco and 2,940,934 to Carlson, among others. Alternatively, conductive particles may be used by taking advantage of charge induced in these particles. The use of both conductive and insulating particles is more fully explained hereinafter.

A pair of insulating blocks or shims 20 and 21 on either side of the backing electrode 11 serve to space this developer coated electrode from the printing member 15 and to establish a definite air gap. In an exemplary pulsing circuit, backing electrode 11 is connected to one output lead of the secondary winding 22 of a transformer 23, the other output lead of the secondary winding being connected to ground. Since the character electrode 12 is also connected to ground, any output voltage induced in the secondary winding 22 of the transformer 23 appears across the two electrodes. The primary winding 25 of transformer 23 is connected in a circuit including a double-pole single-throw switch 26, a DC. power source 27 and a capacitor One terminal of each of power source 27 and capacitor 28 are connected to one side of the primary winding while the opposite sides of the capacitor and power source are connected to the movable contact of the switch and one of the fixed contacts of the switch respectively. Since the second output lead of the primary winding is connected to the other fixed contact of the switch, manipulation of the movable switch contact will connect capacitor 28 either across power source 27 or the primary winding 25. Thus, the power source 27 is used to charge capacitor 28 and it is dischargedacross the primary winding 25 to provide a pulse to the'backing electrode 11 to secondary winding 22. Since the secondary winding 22 of transformer 23 is provided with more turns than the primary winding 25 an increased voltage will be applied to the backing electrode 11. In this particular case the system is arranged to apply a negativepulse to the backing electrode -11. This pulse sets up an intense electric field between electrodes 11 and 12 and since the pulse is negative it repels the negatively charged toner 18 from those areas of the electrode 11 where this field is most intense. Since electric field intensity between two plates is equal to the voltage applied across the plates divided by the distance between the plates, the field intensity in the gap opposite the raised portion 13 of electrode 12 will be significantly higher than that opposite the remaining portions of electrode 12. Thus, the strongest electric field in the gap will be representative of the character to be printed. By applying a pulse of sufficient magnitude to the backing electrode 11 the field opposite the raised character may be made strong enough to repel toner 18 from the backing electrode to the surface 17 of printing member 15 in character configuration, while the field applied to other sections of the toner layer is not large enough to transfer toner. Although as explained hereinafter, the necessary parameters of this TESI-printing technique such as gap spacing, toner charge, and pulse magnitude are mutually dependent, the parameters most often used with this novel technique are very likely to produce an ionizing field discharge in the gap and charge deposition on the printing web because they are above those necessary'for ordinary TESI-printing. When this is considered, the wholeprinting technique of this invention becomes paradoxical. For example, if a negative pulse is applied to the backing electrode to repel negatively charged toner towards the recording web and character electrode, and ionization takes place in the gap, positively charged gas particles or ions -wouldbe attracted towards the backing electrode while negatively charged gas particles (electrons and negative ions) would be attracted towards the relatively positive character electrode, depositing negative charge on the insulating recording web, which should repel the approaching toner. However, when tested, the technique worked admirably and it is presently believed that charged particles of the gaseous atmosphere moving in the gap in the direction opposite to that of'toner movement discharge the toner as it crosses the gap and may even recharge it to the polarity opposite to its original charge, by virtue of collisions between the toner and these charged gas particles.

Alternatively, a positive pulse may be applied to the character electrode 12 to attract the toner particles 18 across the gap. Positively charged toner may also be used in conjunction with a positive repelling charge on the backing electrode 11 or a negative attracting charge on character electrode 12. Conductive toners have also been used in place of charged insulating toners by taking advantage of the charge induced in the toner by the electric field. In this case, either polarity of pulse may be applied to the character electrode to attract the developing material towards the printing member 15 since the pulse will induce charge in the toner prior to moving it towards the printing member. Almost any finely divided conductive material may be used as a conductive developer including copper,

gold, silver, aluminum, etc. Some suitable conductive developers which were tested include carbonyl iron, charcoal powder, and iron filings.

Although gap spacing, pulse duration and magnitude, and the mass of and the charge on the developing material are all interrelated factors, tests using standard xerographie toners were used for printing on CYMAC coated paper with gap spacings ranging from 2 to 7 mils and pulses of from 600 to 2,000 volts ranging up in duration above 1.5 microseconds. It was generally found that pulses of 6 microseconds transferred satisfactory images under all conditions tested so that this was the maximum necessary pulse duration. Although it-is not critical to the process, a pre-conditioning voltage may be applied to the deposited toner layer through the backing electrode to give the toner a strong uniform charge. By applying this pre-conditioning voltage a stronger charge is imparted to the toner resulting in cleaner, sharper prints upon application of the transfer pulse. For example, when a pulse of about 1300 volts was used to transfer toner from the base electrode to the recording web a pre-conditioning voltage of +1200 volts was first applied to the base electrode to charge the toner layer negative and this charging voltage was removed prior to actuation of the device. Biasing voltages ranging down to about +800 volts were also effective for this purpose. When the biasing voltage technique was used with charged insulating toners, the polarity of the voltage was opposite to that of the charge on the toner. Other particle precharging techniques may also'be used in place of the biasing step. For example, a corona generating filament or filament array of the type shown in US. Patents 2,588,699 to Carlson or 2,836,725 to Vyverberg may be spaced above the toner layer to charge the particles to one polarity prior to their selective recharging by the character electrode.

Toner, or developing material, may be deposited on'the backing electrode in many different ways. In the event that an insulating toner is used it'is also desirable that this depositing technique also serve to charge the toner to the correct polarity. Many of the techniques now in use for developing latent electrostatic images in xerography serve admirably for depositingauniform layer of toner on the backing electrode as well as to charge insulating toner if it is used. For example, :a powder cloud. developing apparatus such as those disclosed in US. Patent 2,862,646 to Hayford and 2,918,900 to Carlson, and 2,943,950 to Ricker, are well suited for coating the backing electrode. In addition, this type of device may use insulating or conductive toner interchangeably. Another coating technique which achieved especially good results with insulating toners involves the use of a-two element developing mixture as described in US. Patents 2,618,551 to Walkup, 2,618,552 to Wise, and 2,638,416 to Walkup and Wise. This type of mixture includes toner and carrier beads. As described more fully in the above noted patents the carrier beads are grossly larger than the toner particles and carry these particles to the-surface to be developed, imparting a charge to the particles by virtue of relative positions of the toner particles and carrier beads in the triboelectric series. Thus, the carrier beads pick up the toner particles in the developing mixture and impart a charge to them. When used to develop latent elect-rostatic images in xerography this developing mixture is cascaded over the electrostatic image to be developed and the charge which constitutes the image, by virtue of its.

stronger electric field, pulls toner particles ofi' the carrier beads leaving these particles on the surface being developed in image configuration. When usedin the process of the instant invention the two element developing'mixture described above is dropped from a height of about 68 inches onto the backing electrode surface. When the carrier beads hit the base electrode they bounce clear but'the momentum imparted to the toner particles is sufiicient to shake them loose from the carrier and allow them to stick to the metal base probably by an induction of their own charge into the metal. In this manner a charged uniform layer of toner is deposited on the base electrode.

Almost any conductive material makes a suitable backing electrode and some materials that were successfully used include a 150 mesh stainless steel screen, a smooth brass plate, a grained aluminum or zinc plate, etc. These materials also work well when covered or coated with a thin layer of cellophane which was applied to eliminate any possible mechanical attraction that might exist between the brase electrode and the toner layer. All of these backing electrode materials produced good quality images.

It was also found that improved print quality could be obtained without biasing by using finer toner particles with an average particle size in the 1 to 4 micron range, especially when these particles were deposited on the backing electrode with aluminum carrier beads in place of the ordinary glass carrier beads.

FIGURE 3 which shows an apparatus for applying the printing technique of this invention to a high speed alphanumeric printer, includes a character cylinder 27 which may, for example, contain 40 character columns or rings next to each other along the cylinder surface. Each character column along the cylinder or drum contains a ring of conductive electrodes 28 in the form of the characters to be printed. These may include, for example, all of the letters of the alphabet, the numbers 0-9, and any other arbitrary symbols or characters as desired. Spaced slightly from the drum surface is a backing electrode belt 30 trained around three rollers 31 at least one of which is driven so as to movethe belt at the same peripheral speed as the character cylinder. In this instance the belt is made up of anumber of conductive strips 32 which are electrically separated from each other. The strips are separated by very thin intermediate strips of an insulating material 33. The whole backing electrode belt is covered with toner each time it moves around the rolls 31 as more fully explained in connection with FIGURE 4 below. There is a conductive contact 35 behind each conductive strip 32 of the backing electrode. Each of the contacts 35 is in sliding contact with its associated conductive belt strip. A printing web, which is not shown in FIGURE 3, is normally moved through the gap between the character cylinder 27 and the toner covered backing electrode belt 30 being held closely against the character cylinder. By applying a pulse of the proper magnitude to each of the contacts 35 at the proper time in the rotation of the alphanumeric cylinder 27 a line of selected chanacters may be printed across the printing web by the movement of toner from backing electrode 30 as explained in connection with FIGURES 1 and 2 above. Thus, by proper pulse application to contacts 35, a complete line of print is applied to the printing web and the web is intermittently moved forward a distance equivalent to one line of print between successive li-ne printings.

Because of the very high printing speed cap-abilities of this device it is generally used as the output printer for high speed devices such as analog or digital computers. This type of printer may be tied to the output of a computing device by utilizing a circuitry of the type disclosed in US. Patent 2,919,967 to Schwertz in which case the connections to electrodes 14 and shown in FIGURE 1 of that patent, would be made to contacts 35 as shown in FIGURE 3 of this invention. In this case the character cylinder 27 would also be provided with magnetic pulse generating marks similar to magnetic marks and as shown in the Schwertz patent. Only one character column would be printed for each revolution of the character cylinder so that 40 cylinder revolutions would be required to print a line of print including 40 characters. In the event that it were desired to print a complete line of characters for each revolution of the character cylinder a circuit of the type disclosed in US. Patent 2,776,618 to Hartley would be utilized including appropriate amplifiers where necessary.

FIGURE 4, which is a more detailed side view of the apparatus shown in FIGURE 3, includes a grounded character drum 27 with its associated raised. chanacter electrodes 28. Adjacent to the outer periphery of the character drum is the printing web 36 which comes from web supply roll 37. As stated above, this web is moved intermittently after each line is printed. This movement may be accomplished by using a feeding device similar 'to that used to feed movie film. Adjacent the printing web 37 and just above the printing station there is shown a resistive type heating unit 38 which may be optionally included in the system in order to fuse the developing material to the printing web so as to produce a permanent record. Other fixing techniques such as solvent vapor fixing known to those skilled in the xerographic art may be used as alternatives. This figure also shows belt backing electrode entrained around rollers 31 and cont-acts 35. For illustrative purposes, a potential source 40 and switch 41 are shown for the application of potential to contact 35 although the circuits already described in connection with previous figures are generally used for this purpose. Just above the surface of the belt 30 there is shown a conveyor belt device for coating the backing electrode belt in a manner more fully explained above. The conveyor belt 42 carrying buckets 43 is driven around rollers 44. These buckets pick developer up from container 45 and drop it on the belt from a height of about 6-8 inches. This coats the belt with toner while allowing gravity return of excess toner and carrier beads.

It should be noted at this point that although the backing electrode has been described as an endless be'lt it has also been made in the form of a cylinder of relatively large diameter and can be made in other configurations so as to maintain a relatively uniform spacing between all portions of a character electrode opposite the backing electrode and the surface of the backing electrode. This assures printing of all portions of a selected character since the spacing and resultant electric field opposite each character are then relatively uniform. Generally, the peripheral speed of the backing electrode is the same as that of the alphanumeric drum but it may also be moved intermittently a distance equal to the height of one line of type for each full rotation of the alphanumeric drum.

As stated above, the printing technique of this invention may also be employed in connection with a matrix electrode type printed. A pin matrix system is shown in FIG- URE 5. The matrix 52 substitutes for all of the character electrodes in one of the character columns of the alphanumeric character cylinder shown in FIGURES 3 and 4. As shown in greater detail in FIGURE 6 the pin matrix is made up of a number of conductive pins 53 in five columns and seven rows with each of the pins being electrically separated by an insulating base 46 and separately connected by one of a group of conductors 87 to an activating source. FIGURE 5 also shows a printing web 48, a backing electrode belt 50, and a coating mechanism 51 all of which are similar to those described in connection with FIGURES 3 and 4 above. By choosing selected groups of the pins 45 in the pin matrix electrode 52 for actuation, almost any desired letter or symbol may be printed. For example, the letter L might be printed by actuating the pins in the left-hand column and the pins in the bottom row of the matrix electrode as seen in FIG- URE 6. It also should be noted at this point, that various spacing, shaping, and numbers of electrodes may be used to make up a matrix of the type described here. For example, a matrix might be made up of a group of straight or curved bars, As shown in FIGURE 5 pulses are applied to the pin electrodes and the backing electrode belt is grounded. However, by using a somewhat more com" plex structure the pulses might also be applied through the backing electrode. In this case the conductive portions of the backing electrode belt would have to be themselves in the form of dots and each dot would have to be backed up by a contact when the dots pass by the pin 7 electrode. These contacts might be similar to contacts 35 shown in FIGURES 3 and 4 except that they would have to be quite a bit smaller. I

While the specific embodiments shown and described in this specification and drawings are admirably adapted to fulfill the stated objects, it should be understood that it is not intended to confine the invention to these disclosed embodiments since the invention itself is susceptible of embodiment in many various forms all coming within the scope of the following claims:

What is claimed is:

1. An imaging system comprising in combination a conductive character electrode comprising raised and de-- pressed portions, said raised portions defining a character to be printed, a relatively flat conductive backing electrode spaced from said raised portions on said character electrode to define thereby a gap, means to support an insulating printing member in said gap spaced from said backing electrode, means to deposit solid electroscopic material on the surface of said flat electrode exposed to said gap, and means to apply a potential of from about 600 to about 2,000 volts across said electrodes, said potential being of polarity to move said electroscopic materials from said flat electrode toward said character electrode, forming thereby a pattern of charge corresponding to the configuration of said raised portions of said character electrode on said printing member and causing said electroscopic material opposite the raised portions of said character electrode to move from said flat electrode to said printing member to thereby render the pattern of charge visible.

2. An imaging system comprising in combination a plurality of conductive character electrodes comprising raised and depressed portions, said raised portions defining char- ;acters to be printed, a relatively fiat conductive backing electrode spaced from said raised portions on said char- .acter electrodes to define thereby a gap, means to support an insulating printing member in said gap spaced from said backing electrode, means to deposit solid electroscopic materials on the surface of said flat electrode exposed to said gap, and means to simultaneously apply a potential of from about 600 to 2,000 volts between a selected group of said character electrodes and said relatively fiat backing electrode, forming there-by a pattern of charge corresponding to the configuration of said raised portions of said selected character electrodes on said printing member, and causing said electroscopic material opposite the raised portions of said selected character electrodes to move from said flat electrode to said printing member to thereby render the pattern of charge visible.

References Cited by the Examiner UNITED STATES PATENTS 2,297,691 10/ 1942 Carlson 11717.S X 2,520,504 8/1950 Hooper 101426 2,820,716 1/1958 Harm'on et a1 117-17.5 2,829,025 4/ 1958 Clemens et al. 11717.5 X 2,869,461 1/1959 Jarvis 101-426 2,895,847 7/1959 Mayo 11717.5 2,919,967 1/ 1960 Schwertz 34674 2,996,400 8/1961 Rudd et al. 117-175 3,064,259 11/1962 Schwertz 34674 3,068,481 12/1962 Schwertz 346-74 WILLIAM D. MARTIN, Primary Examiner. 

1. AN IMAGING SYSTEM COMPRISING IN COMBINATION A CONDUCTIVE CHARACTER ELECTRODE COMPRISING RAISED AND DEPRESSED PORTIONS, SAID RAISED PORTIONS DEFINING A CHARACTER TO BE PRINTED, A RELATIVELY FLAT CONDUCTIVE BACKING ELECTRODE SPACE FROM SAID RAISED PORTIONS ON SAID CHARACTER ELECTRODE TO DEFINE THEREBY A GAP, MEANS TO SUPPORT AN INSULATING PRINTING MEMBER IN SAID GAP SPACED FROM SAID BACKING ELECTRODE, MEANS TO DEPOSIT SOLID ELECTROSCOPIC MATERIAL ON THE SURFACE OF SAID FLAT ELECTRODE EXPOSED TO SAID GAP, AND MEANS TO APPLY A POTENTIAL OF FROM ABOUT 6000 TO ABOUT 2,000 VOLTS ACROSS SAID ELECTRODES, SAID POTENTIAL BEING OF POLARITY TO MOVE SAID ELECTROSCOPIC MATERIALS FROM SAID FLAT ELECTRODE TOWARD SAID CHARACTER ELECTRODE, FORMING THEREBY A PATTERN OF CHARGE CORRESPONDING TO THE CONFIGURATION OF SAID RAISED PORTIONS OF SAID CHARACTER ELECTRODE ON SAID PRINTING MEMBER AND CAUSING SAID ELECTROSCOPIC MATERIAL OPPOSITE THE RAISED PORTIONS OF SAID CHARACTER ELECTRODE TO MOVE FROM SAID FLAT ELECTRODE TO SAID PRINTING MEMBER TO THEREBY RENDER THE PATTERN OF CHARGE VISIBLE. 